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## Is there a name for ring elements that multiply to zero?

Let $R$ be a ring (not necessarily with identity). Is there a name for an element $a\in R$ for which $ab=0$ for all $b\in R$? Similarly, for an element $a\in R$ for which $ba=0$ for all $b\in R$? Note, a unital ring has exactly one of each, just zero in both cases, as if $ab=0$ […]

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## What is the probability that the lift safely reaches the ground when there are 10 adults in the lift?

The maximum weight that an elevator in an apartment complex can accommodate is 800kg. The average adult weight be about 70 kgs with a variance of 200. What is the probability that the lift safely reaches the ground when there are 10 adults in the lift?

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## how do you change a 9 by 4 rectangle to a 6 by 6 square?

I know you have to do around the same thing as the 9 by 16 rectangle to a 12 by 12, but I need to know how to make my 9 by 4 into a 6 by 6 with 3 pieces. There are 2 ways. I need the other. If you can, can you please […]

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## Number of possible integers less than 100000 such that the digits 4,5,6 appear in that order

I have been stuck on this problem for some time and I am not sure how to approach it: “How many positive integers less than 100,000 have digits containing 4,5,6 in that particular order?” I am thinking that I would multiply 10X10X3X2X1 since the two of the five digit spaces can hold any digit between […]